The present invention is an improvement over the known 20-roll mill such as is disclosed, among others, in U.S. Pat. No. 2,776,586, FIGS. 1 and 10, hereinafter referred to as ZR Mills, which show a mill with a one-piece housing whose rigid beams each have arcuate channels parallel with the rolls, provided to accommodate spaced "saddles" which carry the roll-backing casters.
Mills built according to that disclosure have amply proven themselves in providing a rigid and precise support for small diameter workrolls--a support unobtainable by other type mills, especially for wide strips and for rolling hard to reduce metals such as stainless and spring steels.
But such mills are confined to a rigid geometry which only allows about 10% for roll wear and a small leeway in workroll diameter. And yet it is highly desirable for investments of this magnitude to provide for some versatility, e.g. a mill that can roll with equal efficiency a 0.030".times.50" stainless steel strip, or a 0.040.times.50" low-carbon autobody sheet with equal ease. This requires a workroll diameter about three times greater. That problem was solved by U.S. Pat. No. 3,147,648 in which the workrolls and all their supporting elements were built into one cylindrical body, the "cartridge", which was pushed into the central opening in the one-piece housing for ultimate support by the rigid beams. The cartridges could be built to any geometry from the smallest rolls for hard steels down to medium and large diameter rolls for soft aluminum or even skinpassing. Yet this mill was too expensive to be accepted. The cost of a cartridge was close to 1/4 of the cost of the mill and at least three were needed as spares for each roll configuration to insure steady production.
Applicant has developed a solution where the mill housing has only one central opening as in the said "cartridge" mill, while various geometry "inserts" are affixed to it. All other expensive elements for supporting the rolls, substantially like those of the ZR Mills can be used interchangeably in conjunction with any rolls.